Photocatalyst comprising titanium fluoride nitride for water decomposition with visible light irradiation

ABSTRACT

A photo-catalyst containing titanium fluoride nitride comprising, Ti(IV)O a N b F c  or a compound represented by MeTi(IV)O a N b F c  prepared by doping at least one metal Me selected from the group consisting of alkalis or alkali metals on Ti(IV)O a N b F c , (wherein,  b  is 0.1 to 1,  c  is 0.1 to 1 and  a  is a value to maintain Ti(IV) and is decided in relation to  b  and  c .). The photo-catalyst containing titanium fluoride nitride is especially characterized by loading at least one promoter selected from the group consisting of Pt, Ni and Pd.

FIELD OF THE INVENTION

The present invention relates to a photo-catalyst containing titaniumfluoride nitride, in particular related to a photo-catalyst which isstable to photo splitting reaction of water having a possibility toreduce a proton to hydrogen or to oxidize water to oxygen by visiblelight.

DESCRIPTION OF THE PRIOR ART

As a technique to carry out catalyst reaction by light, a method toobtain an aimed product by irradiating light to a solid compound whichhas catalytic function and oxidizing or reducing the reaction product bygenerated exiting electron or hole is already known.

Especially, the photo splitting of water is widely interested from theview point of photo energy conversion. Further, the photo catalyst whichdisplays activity to photo splitting reaction of water can be consideredto be an excellent photo functional material possessing functions suchas photo absorption, electrolytic separation or oxidation-reductionreaction at the surface.

Kudo and Kato et al are illustrating that alkali tantalite or alkaliearth is a photo catalyst which displays high activity to the completephoto splitting reaction of water exemplifying many prior arts [forexample, Catal. Letter., 58(1999). 153-155, Chem. Letter., (1999), 1207,Surface, Vol.36, No.12 (1998), 625-645 (shortened to Document A)].

In above mentioned Document A, an useful photo-catalyst material toprogress the splitting reaction of water to hydrogen and/or oxygen isillustrated, and many indications regarding hydrogen generating reactionby reduction of water or oxygen generating reaction by oxidization ofwater and a photo-catalyst for complete photo splitting reaction ofwater are mentioned. Further, said Document A refers to a photo-catalystwhich loads a promoter such as platinum or NiO.

However, a photo-catalyst illustrated in Document A is mainly thephoto-catalyst which contains oxide as a non-metallic element. Further,since the width of the forbidden band of many solid photo-catalystexisting between valence band conduction band, namely, band gap energyis large (≧3 eY), it is hard to act by visible light of lower energy(energy: less than 3 eV). In the meanwhile, almost of conventional solidphoto-catalyst whose gap energy is small and can generate electron andhole by visible light have a problem of photo corrosion under thereacting condition of photo splitting reaction of water. For example, inthe cases of CdS or Cu—ZnS, although the band gap is 2.4 eV, since theseare affected by oxidative photo corrosive action, the catalytic reactionis limited. While, almost of the sun light which reaches to the surfaceof earth is visible light whose energy is small, and for the purpose toprogress the various catalyst reaction, it is necessary to develop aphoto-catalyst which is stable under the condition of photo catalyticreaction. However, unfortunately, there was no photo-catalyst to satisfyabove mentioned requirement up to the present time.

As mentioned above, since almost of sun light which can be utilized atthe surface of earth is visible light, it was necessary to develop aphoto-catalyst which is stable under various reaction conditions ofoxidation and reduction. Almost all of the conventional stablephoto-catalyst are the metal oxide, that is, containing oxide as a nonmetallic element. In the cases of these compounds, since the positionalrelationship between conduction band and valence band from energy viewpoint is largely controlled by energy of valence electron (02 p) orbitof oxygen, band gap energy is large and can not generate photo-catalyticfunction by visible light. Since it was anticipated that the energylevel of valence band is elevated when an element whose valence electronenergy is higher than that of oxygen is reacted with metal and hybridizetheir valence electron orbits, the inventors of the present inventionconsidered if stable compound can be found out among these compoundsunder the photo-catalytic reaction condition, a novel photo-catalystwhich acts by visible light will be able to be generated.

Since the valence electron of nitrogen atom has higher energy than thatof oxygen atom, the band gap energy of metal compound containingnitrogen atom can be make smaller than that of metal oxide and a metaland metal compound which is bonded by adequate amount of nitrogen atomsbecomes possible to generate an excitation electron and a hole byabsorption of visible light of longer wave, and can be a photo-catalystwhich acts by visible light. And the inventors of the present inventionhave continued intensive study to find out a compound which is stableunder the reaction condition among these photo-catalysts, and found outthat the compound composing of oxynitride containing at lease onetransition element can fulfill the function of the photo-catalyst whichsatisfy the above mentioned condition, and already proposed as theinvention which dissolved said problem (JP Application 2000-256681;filed on Aug. 28, 2000). Mostly of these compounds have perovskite-typecrystalline structure, and the stabilizing effect under saidphoto-catalyst reaction condition is conjectured to be caused by thisstructural feature.

As a visible light active compound which was found out based on abovementioned conjecture, although a stable compound can be obtained amongthe compounds containing Ta or Nb, however, it was difficult to obtain astable compound among the compound containing Ti(IV). Therefore, theinventors of the present invention have investigated the method how toobtain a useful compound as the visible light active photo-catalystbased on the theory of above mentioned hybridized oxynitride bondingorbital. In above mentioned consideration, the confirmation ofcharacteristics based on above mentioned theory is considered to beuseful.

The subject of the present invention is to provide a compound which isstable as a visible light active photo-catalyst having nitride bond ofTi(IV), further the object of the present invention is to provide amethod for preparation of said compound. During the variousconsiderations how to introduce a nitride bond into the compoundcontaining Ti(IV), which has photo-catalytic activity, the inventors ofthe present invention found out that the introduction of nitride bond ofTi(IV) is possible when Ti(IV) contains F bond, and found out thesynthesis of the compound containing Ti(IV) which has nitride bond byusing compounds of TiO_(a)N_(b)F_(c) or MeTiO_(a)N_(b)F_(c). And foundthat the obtained compound has a possibility to be a catalyst which isactive by visible light, especially to be a catalyst which generatehydrogen or oxygen by photo splitting of water, thus the subject of thepresent can be accomplished. In the compounds of TiO_(a)N_(b)F_(c) orMeTiO_(a)N_(b)F_(c), Me is an alkali earth metal such as Sr, _(c) is 0.1to 1, _(b) is 0.1 to 1, desirably _(b)≧0.3, and _(a) is a value to bedecided in relation to _(b) and _(c).

By the way, when titanium oxide is nitrided with ammonia by theconventional method, Ti³⁺ is generated by reducing reaction, and whennitride reaction is moderated in order to suppress the reducingreaction, it becomes difficult to introduce sufficient nitrogen intomaterial and the synthesis of the compound containing Ti(IV) which hasnitride bond is impossible, and the responsibility to visible light ofthe material is too low to absorb the visible light of around 600 nm.Accordingly, the method for synthesis of the compound containing Ti(IV)which has nitride bond is an epoch-making invention.

SUMMARY OF THE INVENTION

The first one of the present invention is a photo-catalyst containingtitanium fluoride nitride comprising, Ti(IV)O_(a)N_(b)F_(c) or acompound represented by MeTi(IV)O_(a)N_(b)F_(c) prepared by doping atleast one metal Me selected from the group consisting of alkali oralkaline earth metals on Ti(IV)O_(a)N_(b)F_(c) (wherein, _(b) is 0.1 to1, _(c) is 0.1 to 1 and _(a) is a value to maintain Ti(IV) and isdecided in relation to _(b) and _(c).) Desirably, the present inventionis the photo-catalyst containing titanium fluoride nitride, whereinTi(IV)O_(a)N_(b)F_(c) possesses anataze structure andMeTi(IV)O_(a)N_(b)F_(c) possesses perovskite to anataze structure.Further desirably the present invention is the photo-catalyst containingtitanium fluoride nitride to which at least one promoter selected fromthe group consisting of Pt, Ni and Pd is loaded.

The second one of the present invention is a photo-catalyst for watersplitting containing titanium fluoride nitride comprisingTi(IV)O_(a)N_(b)F_(c) or a compound represented byMeTi(IV)O_(a)N_(b)F_(c) prepared by doping at least one metal Meselected from the group consisting of alkali or alkaline earth metals onTi(IV)O_(a)N_(b)F_(c), (wherein, _(b) is 0.1 to 1, _(c) is 0.1 to 1 and_(a) is a value to maintain Ti(IV) and is decided in relation with _(b)and _(c).). Desirably, the second one of the present invention is aphoto-catalyst for water splitting containing titanium fluoride nitridewherein Ti(IV)O_(a)N_(b)F_(c) possesses anataze structure andMeTi(IV)O_(a)N_(b)F_(c) possesses perovskite to anataze structure.Further desirably the second one of the present invention is aphoto-catalyst for water splitting containing titanium fluoride nitrideto which at least one promoter selected from the group consisting of Pt,Ni and Pd is loaded.

The third one of the present invention is a method for preparation of aphoto-catalyst represented by Ti(IV)O_(a)N_(b)F_(c) (wherein, a, b and care same as to the first one of the present invention) by bakingtitanium di-ammonium fluoride halide containing at least F representedby (HH₄)₂TiF_(d)X_(6-d) (wherein, d is integer of 1-6) and ammoniumhalide by the ratio of equimolar or by the ratio of slightly excess ofammonium halide at the maximum temperature from 200° C. to 500° C.,desirably from 300° C. to 450° C. so as to form a starting material,then said starting material is nitrogenated by thermal synthesis inammonia atmosphere containing from 0.02% to 10.00% of oxygen, air orwater to ammonia by reduced mass to oxygen atom at the maximumtemperature from 350° C. to 700° C., desirably from 400° C. to 600° C.over than 5 hours.

The fourth one of the present invention is a method for preparation of aphoto-catalyst represented by SrTi(IV)O_(a)N_(b)F_(c) (wherein, a, b andc are same as to the first one of the present invention) by bakingtitanium di-ammonium fluoride halide containing at least F representedby TiF_(x)X_(6-X) and/or (HH₄)₂TiF_(d)X_(6-d) (wherein, x and d areinteger of 1-6) and at least one selected from the group consisting ofSrO, SrOH and SrX so as to form a starting material or SrTiF₆, then saidstarting material or SrTiF₆ is nitrogenated by thermal synthesis inammonia atmosphere containing from 0.02% to 10.00% of oxygen, air orwater to ammonia by reduced mass to oxygen atom at the maximumtemperature from 350° C. to 700° C. over than 5 hours.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the X ray diffraction spectrum of the compound of Example 1containing titanium fluoride nitride after nitration.

FIG. 2 is the UV•Visible ray absorption characteristic curve of thecompound of Example 1 containing titanium fluoride nitride afternitration (obtained by diffuse reflectance spectrum. And so forth infollowed Figures).

FIG. 3 shows the change of H₂ generation by time lapse from 10 vol %methanol aqueous solution by visible light longer than 420 nm usingphoto-catalyst prepared by loading 3% of platinum on the compound ofExample 1 containing titanium fluoride nitride after nitration.

FIG. 4 shows the change of O₂ generation by time lapse from AgNO₃aqueous solution by visible light longer than 420 nm using thephoto-catalyst of FIG. 3.

FIG. 5 is the X ray diffraction spectrum of the compound of Example 2containing titanium fluoride nitride after nitration.

FIG. 6 is the UV•Visible ray absorption characteristic curve of thecompound of Example 2 containing titanium fluoride nitride afternitration

FIG. 7 shows the change of H₂ generation by time lapse from 10 vol %methanol aqueous solution by visible light longer than 420 nm usingphoto-catalyst prepared by loading 3% of platinum on the compound ofExample 2 containing titanium fluoride nitride after nitration.

FIG. 8 shows the change of O₂ generation by time lapse from AgNO₃aqueous solution by visible light longer than 420 nm using thephoto-catalyst of FIG. 7.

FIG. 9 is the X ray diffraction spectrum of the compound of Example 3containing titanium fluoride nitride after nitration.

FIG. 10 is the UV•Visible ray absorption characteristic curve of thecompound of Example 3 containing titanium fluoride nitride afternitration.

FIG. 11 shows the change of H₂ generation by time lapse from 10 vol %methanol aqueous solution by visible light longer than 420 nm usingphoto-catalyst prepared by loading 3% of platinum on the compound ofExample 3 containing titanium fluoride nitride after nitration.

FIG. 12 shows the change of O₂ generation by time lapse from AgNO₃aqueous solution by visible light longer than 420 nm using thephoto-catalyst of FIG. 11.

FIG. 13 is the X ray diffraction spectrum of the compound of Example 4containing titanium fluoride nitride after nitration.

FIG. 14 is the UV•Visible ray absorption characteristic curve of thecompound of Example 4 containing titanium fluoride nitride afternitration.

FIG. 15 shows the change of H₂ generation by time lapse from 10 vol %methanol aqueous solution by visible light longer than 420 nm usingphoto-catalyst prepared by loading 3% of platinum on the compound ofExample 4 containing titanium fluoride nitride after nitration.

FIG. 16 shows the change of O₂ generation by time lapse from AgNO₃aqueous solution by visible light longer than 420 nm using thephoto-catalyst of FIG. 15.

FIG. 17 shows the UV•Visible ray absorption characteristic curve ofSrTiONF material of Example 5.

FIG. 18 shows the change of H₂ generation by time lapse from 10 vol %methanol aqueous solution by visible light longer than 420 nm usingphoto-catalyst prepared by loading 1 wt % of platinum on SrTiONFmaterial of Example 5.

FIG. 19 shows the change of O₂ generation by time lapse from AgNO₃aqueous solution by visible light longer than 420 nm using thephoto-catalyst of FIG. 18.

FIG. 20 is the X ray diffraction spectrum of the compound of titaniumdioxide P25 on the market after baked of Comparative Example 1.

FIG. 21 shows the UV•Visible ray absorption characteristic curve of FIG.20.

FIG. 22 is the X ray diffraction spectrum of the nitride compoundprepared by baking titanium dioxide of Comparative Example 2 in theatmosphere of ammonia NH₃ at the maximum temperature 6000° C. for 15hours.

FIG. 23 is the X ray diffraction spectrum of the nitride compound ofFIG. 22.

FIG. 24 shows the X ray diffraction spectrum of strontium titanateSrTiO₃ on the market.

FIG. 25 shows the UV•Visible ray absorption characteristic curve of FIG.24.

FIG. 26 is the X ray diffraction spectrum of the compound prepared bytemperature programmed strontium titanate SrTiO₃ on the market ofComparative Example 4 to 4000° C.(673K) in the atmosphere of ammonia NH₃by temperature-programming speed of 10K/minute then maintain thistemperature for 5 hours.

FIG. 27 shows the UV•Visible ray absorption characteristic curve of FIG.26.

DESCRIPTION OF THE PREFERRED EMBOBYMENT

The present invention will be illustrated more in detail.

A. The photo-catalysts of the present invention can be obtained bysatisfying the essential factors described in the claims.

As the compound having chemical composition of (HH₄)₂TiF_(d)X_(6-d)(wherein, d is integer of 1-6), (HH₄)₂TiF₆ and (HH₄)₂TiF₂XCl₄ can bementioned as the desirable one.

As the material to obtain a starting material to prepare the compoundhaving chemical composition of SrTi(IV)O_(a)N_(b)F_(c), the mixture ofTiF₄ and SrF₂ can be mentioned as the desirable one.

EXAMPLE

The present invention will be illustrated more specifically according tothe Examples, however, not intending to limit the scope of the presentinvention.

Example 1

As the first step, diammonium hexafluorotitanate ((NH₄)₂TiF₆) andammonium chloride (NH₄Cl) were mixed by 1:1 molar ratio. Then themixture was contained into a golden tube and the opening was sealed bywelding. This golden tube was baked at 400° C.(673K) in an electricfurnace for 12 hours. After baking, synthesis by nitration was carriedout under ammonium stream containing oxygen (ammonia flow rate: 0.2dm³·min⁻¹, oxygen flow rate: 1 cm³·min⁻¹) at the temperature of 600°C.(873K) for 12 hours.

Loading of platinum on said material was carried out as follows. Namely,0.00357 dm³ of 0.1 mol 0.1 moldm⁻³ tetraamminedichloro platinumPt(NH₄)₄Cl₂ solution (Pt 3 wt %) was impregnated to 0.3 g of saidmaterial on a water bath and water was evaporated, then reduced byhydrogen at 300° C (573K) for 2 hours.

The X ray diffraction spectrum of the material after baking are shown inFIG. 1. All diffraction peaks in FIG. 1 are belonging to TiNF (refer toPaper: Angew. Chem. Int. Ed. Engle.27 (1988) No.7, p929-930) and thegeneration of TiNF is confirmed. UV•Visible ray absorptioncharacteristic curve of said material (obtained by diffuse reflectancespectrum) is shown in FIG. 2. From FIG. 2, it become clear that saidmaterial absorbs visible light shorter than 600 nm. From the result ofelemental analysis, the ratio of Ti:O:N:F is 1:1.76:0.13:0.10MiO_(1.76)N_(0.18)F_(0.10)).

In FIG. 3 the change of H₂ generation amount by time lapse when 0.2 g ofmaterial to which 3% of platinum is loaded is dispersed in 0.310 dm³ of10 vol. % methanol aqueous solution and visible light longer than 420 nmis irradiated. 300 w xenon lamp is used as the light source and thevisible light shorter than 420 nm is cut off by a cut off filter. Asshown in FIG. 3, it is understood that said material can generatehydrogen constantly from methanol aqueous solution by the irradiation ofvisible light longer than 420 nm. Further, in FIG. 4 the change ofoxygen generation amount by time lapse, when 0.2 g of above material issuspended into 0.310 dm³ of 0.01 moldm⁻³ AgNO₃ aqueous solution andvisible ray longer than 420 nm is irradiated. The reaction is carriedout by same condition mentioned above. From FIG. 4, it become clear thatabove mentioned material can generate oxygen from silver nitrate aqueoussolution under irradiation of visible light longer than 420 nm.

As mentioned above, it is confirmed that TiNF has an ability to reduceproton to hydrogen and to oxidize water to oxygen by visible light whichhas longer wave length than 420 nm.

Example 2

As the first step, diammonium hexafluorotitanate ((NH₄)₂TiF₆) andammonium chloride (NH₄Cl) were mixed by 1:1 molar ratio. Then themixture was contained into a glass tube, vacuumed and the opening wassealed by welding. This glass tube was baked at the temperature of 400°C. (673K) in an electric furnace for 12 hours. After baking, synthesisby nitration was carried out under ammonia stream containing oxygen(ammonia flow rate: 0.04 dm³·min⁻¹, oxygen flow rate: 0.2 cm³·min⁻¹) atthe temperature of 500° C.(773K) for 10 hours. Loading of platinum onsaid material was carried out as follows. Namely, 0.00357 dm³ of 0.1moldm⁻³ tetraamminedichloro platinum Pt(NH₄)₄Cl₂ solution (Pt 3 wt %)was impregnated to 0.3 g of said material on a water bath and water wasevaporated, then reduced by hydrogen at 300° C.(573K) for 2 hours.

The X ray diffraction spectrum of the material after baking are shown inFIG. 5. All diffraction peaks in FIG. 5 are belonging to TiNF (referredto afore mentioned Paper) and the generation of TiNF is confirmed.UV•Visible ray absorption characteristic curve of said material is shownin FIG. 6. From FIG. 6, it become clear that said material absorbsvisible light shorter than 600 nm. From the result of elementalanalysis, the ratio of Ti:O:N:F is 1:1.64:0.14:0.30.

In FIG. 7 the change of H₂ generation amount by time lapse when 0.2 g ofmaterial to which 3 wt % of platinum is loaded is dispersed in 0.310 dm³of 10 vol. % methanol aqueous solution and visible light longer than 420nm is irradiated. 300 w xenon lamp is used as the light source and thevisible light shorter than 420 nm is cut off by a cut off filter. Asshown in FIG. 7, it is understood that said material can generatehydrogen constantly from methanol aqueous solution by the irradiation ofvisible light longer than 420 nm. Further, in FIG. 8 the change ofoxygen generation amount by time lapse, when 0.2 g of above material issuspended into 0.310 dm³ of 0.01 moldm⁻³ AgNO₃ aqueous solution andvisible ray longer than 420 nm is irradiated. The reaction is carriedout by same condition mentioned above. From FIG. 8, it become clear thatabove mentioned material can generate oxygen from silver nitrate aqueoussolution under irradiation of visible light longer than 420 nm.

As mentioned above, it is confirmed that TiNF has an ability to reduceproton to hydrogen and to oxidize water to oxygen by visible light whichhas longer wave length than 420 nm.

Example 3

As the first step, diammonium hexafluorotitanate ((NH₄)₂TiF₆) andammonium chloride (NH₄Cl) were mixed by 1:1 molar ratio. Then themixture was contained into a glass tube, vacuumed and the opening wassealed by welding. This glass tube was baked at 400° C.(673K) in anelectric furnace for 12 hours. After that, further baked at 300°C.(573K) under inert gas stream for 10 hours, then synthesis bynitration was carried out under ammonium stream containing oxygen(ammonia flow rate: 0.2 dm³·min⁻¹, oxygen flow rate: 1 cm³·min⁻¹) at thetemperature of 600° C.(873K) for 15 hours. Loading of platinum on saidmaterial was carried out as follows. Namely, 0.00357 dm³ of 0.1 moldm⁻³tetraamminedichloro platinum Pt(NH₄)₄Cl₂ solution (Pt 3 wt %) wasimpregnated to 0.3 g of said material on a water bath and water wasevaporated, then reduced by hydrogen at 300° C. (573K) for 2 hours.

The X ray diffraction spectrum of the material after baking are shown inFIG. 9. All diffraction peaks in FIG. 9 are belonging to TiNF and thegeneration of TiNF is confirmed. UV•Visible ray absorptioncharacteristic curve of said material is shown in FIG. 10. From FIG. 10,it become clear that said material absorbs visible light shorter than600 nm. From the result of elemental analysis, the ratio of Ti:O:N:F is1:1.74:0.13:0.14.

In FIG. 11 the change of hydrogen generation amount by time lapse when0.2 g of material to which 3 wt % of platinum is loaded is dispersed in0.310 dm³ of 10 vol. % methanol aqueous solution and visible lightlonger than 420 nm is irradiated. 300 w xenon lamp is used as the lightsource and the visible light shorter than 420 nm is cut off by a cut offfilter. As shown in FIG. 11, it is understood that said material cangenerate hydrogen constantly from methanol aqueous solution by theirradiation of visible light longer than 420 nm. Further, in FIG. 12 thechange of oxygen generation amount by time lapse, when 0.2 g of abovematerial is suspended into 0.310 dm³ of 0.01 moldm⁻³ AgNO₃ aqueoussolution and visible ray longer than 420 nm is irradiated. The reactionis carried out by same condition mentioned above. From FIG. 12, itbecome clear that above mentioned material can generate oxygen fromsilver nitrate aqueous solution under irradiation of visible lightlonger than 420 nm.

As mentioned above, it is confirmed that TiNF has an ability to reduceproton to hydrogen and to oxidize water to oxygen by visible light whichhas longer wave length than 420 nm.

Example 4

As the first step, diammonium hexafluorotitanate ((NH₄)₂TiF₆) andammonium chloride (NH₄Cl) were mixed by 1:1 molar ratio. Then themixture was contained into a golden tube, and the opening was sealed bywelding. The sealed golden tube is inserted into a glass tube, saidglass tube was vacuumed and sealed by welding. This glass tube was bakedat 400° C. (673K) in an electric furnace for 12 hours. After that,further baked at 300° C. (573K) under inert gas stream for 10 hours,then synthesis by nitration was carried under ammonia stream (ammoniaflow rate: 0.04 dm³·min⁻¹, dry air flow rate: 0.2 cm³·min⁻¹) at thetemperature of 500° C.(773K) for 10 hours. Loading of platinum on saidmaterial was carried out as follows. Namely, 0.00357 dm³ of 0.1 moldm⁻³tetraamminedichloro platinum Pt(NH₄)₄Cl₂ solution (Pt 3 wt %) wasimpregnated to 0.3 g of said material on a water bath and water wasevaporated, then reduced by hydrogen at 300° C.(573K) for 2 hours.

The X ray diffraction spectrum of the material after baking are shown inFIG. 13. All diffraction peaks in FIG. 13 are belonging to TiNF and thegeneration of TiNF is confirmed. UV•Visible ray absorptioncharacteristic curve of said material is shown in FIG. 10. From FIG. 10,it become clear that said material absorbs visible light shorter than600 nm. From the result of elemental analysis, the ratio of Ti:O:N:F is1:1.45:0.30:0.20.

In FIG. 15 the change of hydrogen generation amount by time lapse when0.2 g of material to which 3 wt % of platinum is loaded is dispersed in0.310 dm³ of 10 vol. % methanol aqueous solution and visible lightlonger than 420 nm is irradiated. 300 w xenon lamp is used as the lightsource and the visible light shorter than 420 nm is cut off by a cut offfilter. As shown in FIG. 15, it is understood that said material cangenerate hydrogen constantly from methanol aqueous solution by theirradiation of visible light longer than 420 nm. Further, in FIG. 16 thechange of oxygen generation amount by time lapse, when 0.2 g of abovematerial is suspended into 0.310 dm³ of 0.01 moldm⁻³ AgNO₃ aqueoussolution and visible ray longer than 420 nm is irradiated. The reactionis carried out by same condition mentioned above. From FIG. 16, itbecome clear that above mentioned material can generate oxygen fromsilver nitrate aqueous solution under irradiation of visible lightlonger than 420 nm.

As mentioned above, it is confirmed that TiNF has an ability to reduceproton to hydrogen and to oxidize water to oxygen by visible light whichhas longer wave length than 420 nm.

Example 5

Titanium fluoride TiF₄ (0.9 g) and strontium fluoride SrF₄ (0.6 g) weremixed together in Ar atmosphere and sealed in a golden tube. This goldentube was further sealed in a Pyrex glass tube in vacuum condition andthe temperature was elevated by temperature-programming speed of10K/minute, then the temperature was maintained at 450° C. for 8 hours.After that cooled down to room temperature and SrTiF₆ was synthesized.The obtained SrTiF₆ was set under ammonia stream containing oxygen(ammonia flow rate: 0.4 dm³·min⁻¹, oxygen flow rate: 0.4 cm³·min⁻¹) andthe temperature was elevated to 673K by temperature-programming speed of10K/minute under ammonia stream of 40 dm³/min flow rate and maintainedfor 5 hours by this temperature. After that the temperature was cooleddown to room temperature and SrTiONF material was synthesized. Accordingto the elemental analysis results, the ratio of Sr:Ti:O:N:F was1:2.35:0.30:0.40. Pt, which is a promoter, was deposited on a catalystby dispersing platinic chloride HPtCl₆ in following reaction solutionthen photo electrodedepositing. Impregnated amount of the promoter canbe adjust in the range from 0.1 to 10 weight %.

UV•Visible ray absorption characteristic curve of said material is shownin FIG. 17. From FIG. 17, it become clear that said material absorbsvisible light shorter than 600 nm. In FIG. 18 the change of hydrogengeneration amount by time lapse when 0.2 g of material to which 1 wt %of platinum is loaded is dispersed in 0.200 dm³ of 10 vol. % methanolaqueous solution and visible light longer than 420 nm is irradiated. 300w xenon lamp is used as the light source and the visible light shorterthan 420 nm is cut off by a cut off filter. As shown in FIG. 18, it isunderstood that said material can generate hydrogen constantly frommethanol aqueous solution by the irradiation of visible light longerthan 420 nm. Further, in FIG. 19 the change of oxygen generation amountby time lapse, when 0.2 g of above material is suspended into 0.200 dm³of 0.01 mol/dm AgNO₃ aqueous solution and visible ray longer than 420 nmis irradiated. The reaction is carried out by same condition mentionedabove. From FIG. 19, it become clear that above mentioned material cangenerate oxygen from silver nitrate aqueous solution under irradiationof visible light longer than 420 nm. From above mentioned results, it isconfirmed that SrTiONF has an ability to reduce proton to hydrogen andto oxidize water to oxygen by visible light which has longer wave lengththan 420 nm.

Comparative Example 1

Titanium dioxide P25, which is the product of Nihon Aerogil was used.Loading of platinum on said material was carried out as follows. Namely,0.00357 dm³ of 0.1 moldm⁻³ tetraamminedichloro platinum Pt(NH₄)₄Cl₂solution (Pt 3 wt %) was impregnated to 0.3 g of said material on awater bath and water was evaporated, then reduced by hydrogen at 300°C.(573K) for 2 hours.

The X ray diffraction spectrum of said material is shown in FIG. 20. InFIG. 20, diffraction peaks of anataze phase and rutile phase can beobserved. UV•Visible ray absorption characteristic curve of saidmaterial is shown in FIG. 21. From FIG. 21, it become clear that saidmaterial absorbs only UV light shorter than 400 nm, and does not absorbvisible light.

The hydrogen generating reaction and oxygen generating reaction werecarried out by same condition to Example 1, however, both hydrogen andoxygen were not generated. From above mentioned results, it is confirmedthat titanium dioxide P25 does not have an ability to reduce proton tohydrogen and to oxidize water to oxygen.

Comparative Example 2

Titanium dioxide was set under ammonia NH₃ stream of flow rate 1dm³·min⁻¹, and the temperature was elevated to 600° C. (873K) bytemperature-programming speed of 10Kmin⁻¹ and baked at this temperaturefor 15 hours, thus nitride was obtained. Loading of platinum on saidmaterial was carried out as follows. Namely, 0.00357 dm³ of 0.1 moldm⁻³tetraamminedichloro platinum Pt(NH₄)₄Cl₂ solution (Pt 3 wt %) wasimpregnated to 0.3 g of said material on a water bath and water wasevaporated, then reduced by hydrogen at 300° C.(573K) for 2 hours.

The X ray diffraction spectrum of said material after baking is shown inFIG. 22. In FIG. 22, anataze phase of titanium dioxide can be observed.UV•Visible ray absorption characteristic curve of said material is shownin FIG. 23. From FIG. 23, it become clear that said material absorbsonly UV light shorter than 400 nm, and does not absorb visible light.

The hydrogen generating reaction and oxygen generating reaction werecarried out by same condition to Example1, however, both hydrogen andoxygen were not generated. From above mentioned results, it is confirmedthat nitride of titanium dioxide does not have an ability to reduceproton to hydrogen and to oxidize water to oxygen.

Comparative Example 3

Strontium titanate SrTiO₃ on the market was used. Pt, which is apromoter, was deposited on a catalyst by dispersing platinic chlorideHPtCl₆ in following reaction solution then photo electrodedepositing.Impregnated amount of the promoter can be adjust in the range from 0.1to 10 weight %.

The X ray diffraction spectrum of said material after baking is shown inFIG. 24. Diffraction peaks in FIG. 24 are confirmed to belong to SrTiO₃.UV•Visible ray absorption characteristic curve of said material is shownin FIG. 25. From FIG. 25, it become clear that said material absorbs UVlight shorter than 370 nm. Same as to Example 1, reactions were carriedout under visible ray irradiation, however, generations of H₂ and O₂were not observed.

Comparative Example 4

Strontium titanate SrTiO₃ on the market was set under ammonia NH₃ streamof flow rate 40 dm/min, and the temperature was elevated to 400° C.(673K) by temperature-programming speed of 10K/min and maintained thistemperature for 5 hours, then the temperature was cooled down to roomtemperature in Ar atmosphere and SrTi(ON)_(x) material was synthesized.Pt, which is a promoter, was deposited on a catalyst by dispersingplatinic chloride HPtCl₆ in following reaction solution then photoelectrodedepositing. Impregnated amount of the promoter can be adjustedin the range from 0.1 to 10 weight %.

The X ray diffraction spectrum of said material after baking is shown inFIG. 26. Diffraction peaks in FIG. 26 are confirmed to belong to SrTiO₃.UV•Visible ray absorption characteristic curve of said material is shownin FIG. 27. From FIG. 27, it become clear that said material absorbsvisible light shorter than 600 nm. However, in longer wave length side,absorption which can be guessed to originate to Ti³⁺ generated byreduction is observed. Same as to Example 1, reactions were carried outunder visible ray irradiation, however, generations of H₂ and O₂ werenot observed.

From above mentioned results, it is understood that even if SrTiO₃ isnitrated in ammonia, the material which has an ability to reduce protonto hydrogen and to oxidize water to oxygen by visible ray having longerwave length than 420 nm can not be obtained.

Industrial Applicability

As mentioned above, the present invention provides the excellent effectthat the compounds of TiO_(a)N_(b)F_(c) or MeTiO_(a)N_(b)F_(c) to whichnitride bond of Ti(IV) is introduced (wherein Me is alkali earth metalsuch as Sr, _(c) is 0.1 to 1, _(b) is 0.1 to 1, desirably b≧3 and _(a)is decided in relation to _(b) and _(c).) have a photo-catalyst activityby visible light.

1. A photo-catalyst containing titanium fluoride nitride comprising,Ti(IV)O_(a)N_(b)F_(c) or a compound represented byMeTi(IV)O_(a)N_(b)F_(c) prepared by doping at least one metal Meselected from the group consisting of alkali or alkaline earth metals onTi(IV)O_(a)N_(b)F_(c), wherein, b is 0.1 to 1, c is 0.1 to 1 and a is avalue to maintain Ti(IV) and is decided in relation to b and c.
 2. Thephoto-catalyst containing titanium fluoride nitride of claim 1 to whichat least one promoter selected from the group consisting of Pt, Ni andPd is loaded.
 3. The photo-catalyst containing titanium fluoride nitrideof claim 1, wherein Ti(IV)O_(a)N_(b)F_(c) possesses anataze structureand MeTi(IV)O_(a)N_(b)F_(c) possesses perovskite to anataze structure.4. The photo-catalyst containing titanium fluoride nitride of claim 3 towhich at least one promoter selected from the group consisting of Pt, Niand Pd is loaded.
 5. A photo-catalyst for water splitting containingtitanium fluoride nitride comprising, Ti(IV)O_(a)N_(b)F_(c) or acompound represented by MeTi(IV)O_(a)N_(b)F_(c) prepared by doping atleast one metal Me selected from the from the group consisting of alkalior alkaline earth metals on Ti(IV)O_(a)N_(b)F_(c), wherein, b is 0.1 to1, c is 0.1 to 1 and a is a value to maintain Ti(IV) and is decided inrelation with b and c.
 6. The photo-catalyst for water splittingcontaining titanium fluoride nitride of claim 5 to which at least onepromoter selected from the group consisting of Pt, Ni, Ru and Pd isloaded.
 7. The photo-catalyst for water splitting containing titaniumfluoride nitride of claim 5, wherein Ti(IV)O_(a)N_(b)F_(c) possessesanataze structure and MeTi(IV)O_(a)N_(b)F_(c) possesses perovskite toanataze structure.
 8. The photo-catalyst for water splitting containingtitanium fluoride nitride of claim 7 to which at least one promoterselected from the group consisting of Pt, Ni and Pd is loaded.
 9. Amethod for preparation of a photo-catalyst represented byTi(IV)O_(a)N_(b)F_(c), wherein a, b and c are same as to claim 1 bybaking titanium di-ammonium fluoride halide represented by(HH₄)₂TiF_(d)X_(6-d), wherein, d is of 1-6, which contains at least Fand ammonium halide by the ratio of equimolar or by the ratio ofslightly excess of ammonium halide at the maximum temperature from 200to 500 so as to form a starting material, then said starting material isnitrogenated by thermal synthesis in ammonia atmosphere containing from0.02% to 10.00% of oxygen, air or water to ammonia by reduced mass tooxygen atom at the maximum temperature from 350 to 700 for over than 5hours.
 10. A method for preparation of a photo-catalyst represented bySrTi(IV)O_(a)N_(b)F_(c), wherein, a, b and c are same as to claim 1, bybaking titanium di-ammonium fluoride halide represented byTiF_(x)X_(6-x) and/or (HH₄)₂TiF_(d)X_(6-d), wherein x and d are 1-6,which contains at least F and at least one compound selected from thegroup consisting of SrO, SrOH and SrX so as to form a starting materialor SrTiF₆, then said starting material or SrTiF₆ is nitrogenated bythermal synthesis in ammonia atmosphere containing from 0.02% to 10.00%of oxygen, air or water to ammonia by reduced mass to oxygen atom at themaximum temperature from 350 to 700 for over than 5 hours.